A milling machine including a mill as means for grating an object to be grated such as tea leaves and cereals has conventionally been used. The milling machine obtains powders by finely grating an object to be grated between an upper mill and a lower mill constituting the mill. For example, Japanese Patent Laying-Open No. 2000-000478 (PTD 1) and Japanese Patent Laying-Open No. 2011-172491 (PTD 2) disclose such a milling machine.
A milling machine including a grating portion such as a mill as means for grating an object to be grated such as tea leaves and cereals has conventionally been used. The milling machine obtains powders by finely grating an object to be grated between grating members arranged to be opposed to each other along a vertical direction. For example, Japanese Patent Laying-Open No. 2013-39206 (PTD 3) and Japanese Patent Laying-Open No. 2004-17010 (PTD 4) disclose such a milling machine.
In the milling machine disclosed in PTD 3, powders produced by the grating portion which grates an object to be grated are discharged to an annular powder feed path defined by a passage wall arranged to cover the entire outer circumferential surface of the grating portion. The powders discharged to the powder feed path are discharged to the outside as a movable portion of a collection and discharge portion which collects the powders and discharges the powders to the outside moves through the path. The milling machine includes drive means which drives the grating portion and the movable portion and grounding means for grounding the passage wall formed of a conductive material, the grounding means removing charges in the passage wall and the grating portion which are charged.
In the milling machine disclosed in PTD 4, a reception surface which carries powders discharged from between grating surfaces of the upper mill and the lower mill is formed around the entire outer circumference at an upper end of the mill and an outlet is provided in a part in a circumferential direction of an upper portion of the lower mill. As the upper mill rotates, the powders carried on the reception surface of the upper mill are discharged from the outlet. Since the powders on the reception surface can be discharged without using a spatula member made of a synthetic resin, electrostatic charging can be suppressed.
A milling machine including a mill as means for grating an object to be grated such as a woody material, tea leaves, and cereals has conventionally been used. The milling machine obtains powders by finely grating an object to be grated between an upper mill and a lower mill constituting the mill.
For example, Japanese Patent Laying-Open No. 2006-312136 (PTD 5) and Japanese Patent Laying-Open No. 2013-183647 (PTD 6) disclose such a milling machine including a mill.
In the mill provided in the milling machine disclosed in PTD 5, a plurality of grooves extending in parallel in a prescribed direction are provided in each divided region resulting from division of a grinding surface into six portions with the center of rotation being defined as the reference. The plurality of grooves are provided such that a width is greater every prescribed number of grooves. With such a construction, a woody material containing a large amount of fibers can suitably be grated.
In the mill provided in the milling machine disclosed in PTD 6, a grinding surface of the upper mill is provided with a projection portion having such a curved shape as projecting toward the lower mill, and a grinding surface of the lower mill is provided with a projection portion in a substantially trapezoidal shape in a cross-sectional view which projects such that an inclination on an inner circumferential side is more acute than an inclination on an outer circumferential side. The projection portion in the upper mill is different in size (depth and width) from the projection portion in the lower mill. With such a construction, powders various in size such as powders greater in grain size and powders smaller in grain size can be obtained.